Process for making a décor paper having improved optical performance

ABSTRACT

A décor paper is prepared from a dispersion having improved optical performance, wherein the dispersion contains a TiO2 particle slurry; paper pulp; and a cationic polymer. The TiO2 particle slurry has a treated TiO2 particle with a surface area of at least about 30 m2/g and a cationic polymer; the treatment is an oxide of silicon, aluminum, phosphorus or mixtures thereof; and the treatment is present in the amount of at least 15% based on the total weight of the treated titanium dioxide particle. Comparable dispersions not using the TiO2 particle slurry described would require about 10% more treated TiO2 particle than a dispersion made with the described TiO2 particle slurry, paper pulp, and cationic polymer to achieve equivalent optical performance. These décor papers are useful in preparing paper laminates.

BACKGROUND OF THE DISCLOSURE

The present disclosure pertains to a décor paper and paper laminatesmade from such paper. More specifically, the décor paper comprises atreated inorganic core particle, in particular a treated titaniumdioxide particle, having improved opacity in highly loaded papersystems.

Paper laminates are in general well-known in the art, being suitable fora variety of uses including table and desk tops, countertops, wallpanels, floor surfacing, and the like. Paper laminates have such a widevariety of uses because they can be made to be extremely durable, andcan be also made to resemble (both in appearance and texture) a widevariety of construction materials, including wood, stone, marble andtile, and they can be decorated to carry images and colors.

Typically, the paper laminates are made from décor paper by impregnatingthe paper with resins of various kinds, assembling several layers of oneor more types of laminate papers, and consolidating the assembly into aunitary core structure while converting the resin to a cured state. Thetype of resin and laminate paper used, and composition of the finalassembly, are generally dictated by the end use of the paper laminate.

Decorative paper laminates can be made by utilizing a decorated paperlayer as the visible paper layer in the unitary core structure. Theremainder of the core structure typically comprises various supportpaper layers, and may include one or more highly-opaque intermediatelayers between the decorative and support layers so that the appearanceof the support layers does not adversely impact the appearance ofdecorative layer.

Paper laminates may be produced by both low- and high-pressurelamination processes.

Décor papers typically comprise fillers such as titanium dioxide toincrease brightness and opacity to the paper. Typically, these fillersare incorporated into the fibrous paper web by wet end addition.

In light colored and bright white décor paper applications, TiO₂concentrations of 30-45% by weight of pigment are needed to provide thedesired color and/or opacity. However, at these high loading levels, theefficiency at which TiO₂ functions as an opacifying agent deterioratesdue to the “crowding effect” of the pigment. That is, twice the amountof pigment use based on a less concentrated paper system (i.e. one thatcomprises 20% TiO₂ by weight), will not double the opacity in a highlyloaded paper. In fact, the opacity falls short due to the crowdingeffect. Hence décor paper manufactures incur a cost penalty to reach thedesired opacity in highly loaded white papers. Thus the need exists fora TiO₂ pigment that can maintain its opacifying efficiency even inhighly loaded paper systems.

SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a dispersion for making décorpaper having improved optical performance without negatively impactingpaper mechanical strength comprising:

-   -   (a) a TiO₂ pigment slurry comprising a treated TiO₂ pigment        having a surface area of at least about 30 m²/g, and a cationic        polymer; wherein the treatment comprises an oxide of silicon,        aluminum, phosphorus or mixtures thereof; and the treatment is        present in the amount of at least 15% based on the total weight        of the treated titanium dioxide pigment;    -   (b) paper pulp; and    -   (c) a cationic polymer; wherein the cationic polymer in the        slurry and the cationic polymer in the dispersion are        compatible; wherein for equal optical performance, the amount of        treated TiO₂ pigment in the dispersion is reduced by about 10%        when compared to a dispersion not comprising the treated TiO₂        pigment of (a).

In the first aspect, the cationic polymer in the slurry is aurea-formaldehyde resin, a melamine-formaldehyde resin, a cationicpolyacrylamide polymer, a polydialkyllammonium polymer, apolyacrylamide-polydialkylammonium copolymer, or apolyamide-polyamine-epichlorhydrin resin.

In the first aspect, the cationic polymer in the dispersion (c) is aurea-formaldehyde resin, a melamine-formaldehyde resin or apolyamide-polyamine-epichlorhydrin resin.

In a second aspect, the disclosure provides a décor paper comprising adispersion having improved optical performance without negativelyimpacting mechanical paper strength comprising:

-   -   (a) a TiO₂ pigment slurry comprising a treated TiO₂ pigment        having a surface area of at least about 30 m²/g, and a cationic        polymer; wherein the treatment comprises an oxide of silicon,        aluminum, phosphorus or mixtures thereof; and the treatment is        present in the amount of at least 15% based on the total weight        of the treated titanium dioxide pigment;    -   (b) paper pulp; and    -   (c) a cationic polymer; wherein the cationic polymer in the        slurry and the cationic polymer in the dispersion are        compatible; wherein for equal optical performance, the amount of        treated TiO₂ pigment in the dispersion is reduced by about 10%        when compared to a dispersion not comprising the treated TiO₂        pigment of (a).

In a third aspect, the disclosure provides a paper laminate comprising adécor paper wherein the décor paper comprises a dispersion havingimproved optical performance without negatively impacting mechanicalpaper strength comprising:

-   -   (d) a TiO₂ pigment slurry comprising a treated TiO₂ pigment        having a surface area of at least about 30 m²/g, and a cationic        polymer; wherein the treatment comprises an oxide of silicon,        aluminum, phosphorus or mixtures thereof; and the treatment is        present in the amount of at least 15% based on the total weight        of the treated titanium dioxide pigment;    -   (e) paper pulp; and    -   (f) a cationic polymer; wherein the cationic polymer in the        slurry and the cationic polymer in the dispersion are        compatible; wherein for equal optical performance, the amount of        treated TiO₂ pigment in the dispersion is reduced by about 10%        when compared to a dispersion not comprising the treated TiO₂        pigment of (a).

In the second aspect, the disclosure provides a paper laminate furthercomprising kraft paper.

DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure “comprising” is to be interpreted as specifying thepresence of the stated features, integers, steps, or components asreferred to, but does not preclude the presence or addition of one ormore features, integers, steps, or components, or groups thereof.Additionally, the term “comprising” is intended to include examplesencompassed by the terms “consisting essentially of” and “consistingof.” Similarly, the term “consisting essentially of” is intended toinclude examples encompassed by the term “consisting of.”

In this disclosure, when an amount, concentration, or other value orparameter is given as either a range, typical range, or a list of uppertypical values and lower typical values, this is to be understood asspecifically disclosing all ranges formed from any pair of any upperrange limit or typical value and any lower range limit or typical value,regardless of whether ranges are separately disclosed. Where a range ofnumerical values is recited herein, unless otherwise stated, the rangeis intended to include the endpoints thereof, and all integers andfractions within the range. It is not intended that the scope of thedisclosure be limited to the specific values recited when defining arange.

In this disclosure, terms in the singular and the singular forms “a,”“an,” and “the,” for example, include plural referents unless thecontent clearly dictates otherwise. Thus, for example, reference to“TiO₂ particle”, “the TiO₂ particle”, or “a TiO₂ particle” also includesa plurality of TiO₂ particles.

This disclosure relates to an inorganic core particle, typicallyinorganic metal oxide or mixed metal oxide pigment particles, moretypically a titanium dioxide particle that may be a pigment or ananoparticle, wherein the inorganic core particles, typically inorganicmetal oxide or mixed metal oxide particles, more typically titaniumdioxide particles having improve opacity in highly loaded paper systems.

Titanium Dioxide Particle:

It is contemplated that the titanium dioxide particle, and in particulartitanium dioxide pigment particles are treated as per this disclosure.The total amount of the treatment which may be an oxide of silicon,aluminum, or mixtures thereof is at least about 15%, based on the totalweight of the treated titanium dioxide particle. Typically the silicatreatment level is at least about 6%, more typically about 6-about 14%,and still more typically about 9.5 about 12%. The alumina treatmentlevel is about 4-about 8%, more typically about 5.5 to about 6%, basedon the total weight of the treated titanium dioxide particle. Bytitanium dioxide particle it is meant a particulate material thatbecomes dispersed throughout a final product such as a paper laminatecomposition and imparts color and opacity to it. More typically, thetitanium dioxide (TiO₂) particle is pigmentary.

Titanium dioxide (TiO₂) particles useful in the present disclosure maybe in the rutile or anatase crystalline form. They are commonly made byeither a chloride process or a sulfate process. In the chloride process,TiCl₄ is oxidized to TiO₂ particles. In the sulfate process, sulfuricacid and ore containing titanium are dissolved, and the resultingsolution goes through a series of steps to yield TiO₂. Both the sulfateand chloride processes are described in greater detail in “The PigmentHandbook”, Vol. 1, 2nd Ed., John Wiley & Sons, NY (1988), the teachingsof which are incorporated herein by reference. The particle may be apigment or nanoparticle, more typically pigment.

By “pigment” it is meant that the titanium dioxide particles have anaverage size of less than 1 micron. Typically, the particles have anaverage size of from about 0.020 to about 0.95 microns, more typically,about 0.050 to about 0.75 microns and most typically about 0.075 toabout 0.50 microns. By “nanoparticle” it is meant that the primarytitanium dioxide particles have a median primary particle size ofgreater than about 70 nm, more typically about 70 nm to about 135 nm andstill more typically about 90 nm to about 120 nm. Dynamic lightscattering, an optical technique that measures the particle sizedistribution in liquid suspension, shows that typically 80% of producedparticles have diameters less than 164 nm.

Process for Preparing Treated Titanium Dioxide Particles

In one embodiment, the process for preparing a treated titanium dioxide(TiO₂) particle having improved opacity comprises heating a slurrycomprising porous silica treated titanium dioxide particle and water ata temperature of at least about 90° C., more typically about 93 to about97° C., still more typically about 95 to about 97° C. The silicaapplication can be by deposition of pyrogenic silica onto pyrogenictitanium dioxide particle, or by co-oxygenation of silicon tetrachloridewith titanium tetrachloride, or by deposition via condensed phaseaqueous oxide.

In a specific embodiment, the slurry comprising silica treated titaniumdioxide particle and water is prepared by a process comprising thefollowing steps that include providing a slurry of titanium dioxideparticle in water; wherein typically TiO₂ is present in the amount of 25to about 35% by weight, more typically about 30% by weight, based on thetotal weight of the slurry. This is followed by heating the slurry toabout 30 to about 40° C., more typically 33-37° C., and adjusting the pHto about 3.5 to about 7.5, more typically about 5.0 to about 6.5.Soluble silicates such as sodium or potassium silicate are then added tothe slurry while maintaining the pH between about 3.5 and about 7.5,more typically about 5.0 to about 6.5; followed by stirring for at leastabout 5 min and typically at least about 10 minutes, but no more than 15minutes, to facilitate silica precipitation onto the titanium dioxideparticle. Commercially available water soluble sodium silicates withSiO₂/Na₂O weight ratios from about 1.6 to about 3.75 and varying from 32to 54% by weight of solids, with or without further dilution are themost practical. To apply a porous silica to the titanium dioxideparticle, the slurry should typically be acidic during the addition ofthe effective portion of the soluble silicate. The acid used may be anyacid, such as HCl, H₂SO₄, HNO₃ or H₃PO₄ having a dissociation constantsufficiently high to precipitate silica and used in an amount sufficientto maintain an acid condition in the slurry. Compounds such as TiOSO₄ orTiCl₄ which hydrolyze to form acid may also be used. Alternative toadding the entire acid first, the soluble silicate and the acid may beadded simultaneously as long as the acidity of the slurry is typicallymaintained at a pH of below about 7.5. After addition of the acid, theslurry should be maintained at a temperature of no greater than 50° C.for at least 30 minutes before proceeding with further additions.

The treatment corresponds to about 6 to about 14% by weight of silica,more typically about 9.5 to about 12.0%, and still more typically 10.5%based on the total weight of the titanium dioxide particle, and inparticular the titanium dioxide core particle. The amounts of deposited(non-metal and metal) oxides allow control of the isoelectric pointbetween 5.0 and 7.0 which can be beneficial in facilitating thedispersion and/or flocculation of the particulate compositions duringplant processing and décor paper production.

An alternate method of adding a silica treatment to the TiO₂ particle isby deposition of pyrogenic silica onto pyrogenic titanium dioxideparticle, as described in U.S. Pat. No. 5,992,120, or by co-oxygenationof silicon tetrachloride with titanium tetrachloride, as described inU.S. Pat. No. 5,562,764, and U.S. Pat. No. 7,029,648 which areincorporated herein by reference.

The slurry comprising dense silica treated titanium dioxide particlesand water is heated at a temperature of at least about 90° C., moretypically about 93 to about 97° C., still more typically about 95 toabout 97° C. The second treatment comprises precipitated aluminum oxideor alumina. This treatment is porous, and is typically applied from asolution of soluble alumina source, such as a soluble aluminate, usingtechniques known to one skilled in the art. In a specific embodiment, asoluble alumina source, such as a soluble aluminate, is added to theslurry comprising silica treated titanium dioxide while maintaining thepH at about 7.0 to 10.0, more typically 8.5 to about 9.5 to form analumina treatment on the porous silica treated titanium dioxideparticle. By “soluble alumina source” is meant alkali metal salts ofaluminate anions, for example, sodium or potassium aluminate.Alternatively, the soluble alumina source may be acidic, such as forexample aluminum chloride or aluminum sulfate, in which case the pH iscontrolled using a base rather than an acid. The treated titaniumdioxide particle does not comprise dense silica or alumina treatments.

The porous alumina treatment is present in the amount of about 4.0% toabout 8.0%; more typically about 5.0% to about 7.5%, still moretypically 5.8% based on the total weight of the titanium dioxideparticle. Because substantially all of the alumina that is precipitatedfinds its way to a treatment on the titanium dioxide particles, ittypically is only necessary to provide that amount of soluble aluminasource, such as a soluble aluminate, to the slurry liquid which willresult, after precipitation, in the appropriate degree of treatment

Typically, the particle to particle surface treatments are substantiallyhomogenous. By this we mean that each core particle has attached to itssurface an amount of alumina and silica such that the variability inalumina and silica levels among particles is so low as to make allparticles interact with water, organic solvent or dispersant moleculesin the same manner (that is, all particles interact with their chemicalenvironment in a common manner and to a common extent). Typically, thetreated titanium dioxide particles are completely dispersed in the waterto form a slurry in less than 10 minutes, more typically less than about5 minutes. By “completely dispersed” we mean that the dispersion iscomposed of individual particles or small groups of particles createdduring the particle formation stage (hard aggregates) and that all softagglomerates have been reduced to individual particles.

After treatment according to this process the pigment is recovered byknown procedures including neutralization of the slurry and ifnecessary, filtration, washing, drying and frequently a dry grindingstep such as micronizing. Drying is not necessary, however, as a thickslurry of the product can be used directly in preparing paperdispersions where water is the liquid phase.

Applications

The treated titanium dioxide particles may be used in paper laminates.The paper laminates of this disclosure are useful as flooring,furniture, countertops, artificial wood surface, and artificial stonesurface.

Décor Paper

Décor paper may contain fillers such as titanium dioxide prepared asdescribed above and also additional fillers. Some examples of otherfillers include talcum, zinc oxide, kaolin, calcium carbonate andmixtures thereof.

The filler component of the decorative paper can be about 10 to about65% by weight, in particular 30 to 45% by weight, based on the totalweight of the décor paper. The basis weight of the décor paper base canbe in the range of 30 to about 300 g/m², and in particular 90 to 110g/m². The basis weights are selected as a function of the particularapplication.

Coniferous wood pulps (long fiber pulps) or hardwood pulps such aseucalyptus (short fibered pulps) and mixtures thereof are useful aspulps in the manufacture of décor paper base. It is also possible to usecotton fibers or mixtures all these types of pulps. A mixture ofconiferous wood and hardwood pulps in a ratio of about 10:90 to about90:10, and in particular about 30:70 to about 70:30 can be useful. Thepulp can have a degree of beating of 20° to about 60° SR according toSchopper-Riegler.

The décor paper may also contain a cationic polymer that may comprise anepichlorohydrin and tertiary amine or a quaternary ammonium compoundsuch as chlorohydroxypropyl trimethyl ammonium chloride or glycidyltrimethyl ammonium chloride. Most typically the cationic polymer is aquaternary ammonium compound. Cationic polymers such as wet strengthenhancing agents that include polyamide/polyamine epichlorohydrinresins, other polyamine derivatives or polyamide derivatives, cationicpolyacrylates, modified melamine formaldehyde resins or cationizedstarches are also useful and can be added to form the dispersion. Otherresins include, for example, diallyl phthalates, epoxide resins, ureaformaldehyde resins, urea-acrylic acid ester copolyesters, melamineformaldehyde resins, melamine phenol formaldehyde resins, phenolformaldehyde resins, poly(meth)acrylates and/or unsaturated polyesterresins. The cationic polymer is present in the amount of about 0.5 toabout 1.5%, based on the dry polymer weight to the total dry weight pulpfibers used in the paper.

Retention aids, wet-strength, retention, sizing (internal and surface)and fixing agents and other substances such as organic and inorganiccolored pigments, dyes, optical brighteners and dispersants may also beuseful in forming the dispersions and may also be added as required toachieve the desired end properties of the paper. Retention aids areadded in order to minimize losses of titanium dioxide and other finecomponents during the papermaking process, which adds cost, as do theuse of other additives such as wet-strength agents.

Examples of papers used in paper laminates may be found in U.S. Pat. No.6,599,592 (the disclosure of which is incorporated by reference hereinfor all purposes as if fully set forth) and the above-incorporatedreferences, including but not limited to U.S. Pat. No. 5,679,219, U.S.Pat. No. 6,706,372 and U.S. Pat. No. 6,783,631.

As indicated above, the paper typically comprises a number of componentsincluding, for example, various pigments, retention agents andwet-strength agents. The pigments, for example, impart desiredproperties such as opacity and whiteness to the final paper, and acommonly used pigment is titanium dioxide that is, in a relative sense,expensive in nature.

The treated titanium dioxide particle can be used to prepare the décorpaper in any of the customary ways, wherein at least a portion of thetitanium dioxide pigment typically used in such papermaking is replacedwith the treated titanium dioxide pigment.

As indicated above, the décor paper in accordance with the presentdisclosure is an opaque, cellulose pulp-based sheet containing atitanium dioxide pigment component in an amount of about 45 wt % orless, more typically from about 10 wt % to about 45 wt %, and still moretypically from about 25 wt % to about 42 wt %, wherein the titaniumdioxide pigment component comprises the treated titanium dioxideparticle of this disclosure. In one typical embodiment, the titaniumdioxide pigment component comprises at least about 25 wt %, and moretypically at least about 40 wt % (based on the weight of the titaniumdioxide pigment component) of the treated titanium dioxide pigment ofthis disclosure. In another typical embodiment, the titanium dioxidepigment component consists essentially of the treated titanium dioxidepigment of this disclosure. In yet another typical embodiment, thetitanium dioxide pigment component comprises substantially only thetreated titanium dioxide pigment of this disclosure.

Paper Laminates

Paper laminates in accordance with the present disclosure can be made byany of the conventional processes well known to those of ordinary skillin the relevant art, as described in many of the previously incorporatedreferences.

Typically, the process of making paper laminates begins with rawmaterials—impregnating resins such as phenolic and melamine resins,brown paper (such as kraft paper) and high-grade print paper (a laminatepaper in accordance with the present disclosure).

The brown paper serves as a carder for the impregnating resins, andlends reinforcing strength and thickness to the finished laminate. Thehigh-grade paper is the decorative sheet, for example, a solid color, aprinted pattern or a printed wood grain.

In an industrial-scale process, rolls of paper are typically loaded on aspindle, at the “wet end” of a resin treater for impregnation with aresin. The high-grade (decorative) surface papers are treated with aclear resin, such as melamine resin, so as to not affect the surface(decorative) appearance of the paper. Since appearance is not criticalfor the brown paper, it may be treated with a colored resin such asphenolic resin.

Two methods are commonly used to impregnate the paper with resin. Theusual way (and the fastest and most efficient) is called “reverse-rollcoating.” In this process, the paper is drawn between two big rollers,one of which applies a thin coating of resin to one side of the paper.This thin coating is given time to soak through the paper as it passesthrough to a drying oven. Almost all of the brown paper is treated bythe reverse-roll process, because it is more efficient and permits fullcoating with less resin and waste.

Another way is a “dip and squeeze” process, in which the paper is drawnthrough a vat of resin, and then passed through rollers that squeeze offexcess resin. The surface (decorative) papers are usually resinimpregnated by the dip-and-squeeze process because, although slower, itpermits a heavier coating of the impregnating resin for improvingsurface properties in the final laminate, such as durability andresistance to stains and heat.

After being impregnated with resin, the paper (as a continuous sheet) ispassed through a drying (treater) ovens to the “dry end,” where it iscut into sheets.

The resin-impregnated paper should have a consistent thickness to avoidunevenness in the finished laminate.

In the assembly of the laminate components, the top is generally thesurface paper since what the finished laminate looks like depends mainlyon the surface paper. A topmost “overlay” sheet that is substantiallytransparent when cured may, however, be placed over the decorativesheet, for example, to give depth of appearance and wear resistance tothe finished laminate.

In a laminate where the surface paper has light-hued solid colors, anextra sheet of fine, white paper may be placed beneath the printedsurface sheet to prevent the amber-colored phenolic filler sheet frominterfering with the lighter surface color.

The texture of the laminate surface is determined by textured paperand/or a plate that is inserted with the buildup into the press.Typically, steel plates are used, with a highly polished plate producinga glossy finish, and an etched textured plate producing a matte finish.

The finished buildups are sent to a press, with each buildup (a pair oflaminates) is separated from the next by the above-mentioned steelplate. In the press, pressure is applied to the buildups by hydraulicrams or the like. Low and high pressure methods are used to make paperlaminates. Typically, at least 800 psi, and sometimes as much as 1,500psi pressure is applied, while the temperature is raised to more than250° F. by passing superheated water or steam through jacketing builtinto the press. The buildup is maintained under these temperature andpressure conditions for a time (typically about one hour) required forthe resins in the resin-impregnated papers to re-liquefy, flow and cure,bonding the stack together into a single sheet of finished, decorativelaminate.

Once removed from the press, the laminate sheets are separated andtrimmed to the desired finished size. Typically the reverse side of thelaminate is also roughened (such as by sanding) to provide a goodadhesive surface for bonding to one or more substrates such as plywood,hardboard, particle board, composites and the like. The need for andchoice of substrate and adhesive will depend on the desired end use ofthe laminate, as will be recognized by one of ordinary skill in therelevant art.

The examples which follow, description of illustrative and typicalembodiments of the present disclosure are not intended to limit thescope of the disclosure. Various modifications, alternativeconstructions and equivalents may be employed without departing from thetrue spirit and scope of the appended claims.

EXAMPLES Example 1

Process for Making Cationized Titanium Dioxide Slurry.

A 35 wt. % aqueous slurry was made by charging a 500 mL stainless steelbeaker with 156.6 g of demineralized water, 5.9 g of a 38% polyaluminumchloride solution, and 4.28 g of Kymene 617, a commercially availablewet strength resin (WSR). The pH of this solution measured 3.28. 45 g ofTiO₂ pigment (half of the total pigment addition) was added withstirring to make a pigment slurry. The pH was adjusted to 3.5 with 10%HCl. The remaining 45 g of TiO₂ pigment was added with stirring. The pHwas adjusted upward to 5.0 by the addition of 10% NaOH solution. Theisoelectric point (IEP) of 8.4 was measured for the pigment containedwithin.

Incorporating TiO2 Slurry into a Décor Paper Composition.

A stock mixture of paper pulp slurry was made by combining 45 g. of dryeucalyptus pulp in 1455 g of demineralized water (i.e. 3% solids). Themixture was further homogenized in a pulp disintegrator and theresulting slurry diluted to 0.625% solids with the addition of 7.2 L ofdemineralized water in an equalizer vessel. pH of the pulp slurrymeasured 5.7.

Hand Sheet Formation.

Hand sheets were formulated for basis weights of 100-115 g/m²corresponding to a ladder of TiO₂ content ranging from 22-41%. ActualTiO₂ content of hand sheets was determined from the ash content of thepaper. In a typical preparation, hand sheets containing 40% TiO₂ werefabricated by combining 339 g of pulp suspension with 5.7 g ofcationized TiO₂ dispersion (from above) using low shear agitation. pH ofthis mixture was adjusted upward to pH 7.4 with 10% NaOH to inducepigment flocculation. An additional aliquot of Kymene WSR was added tothe paper furnish to compensate for the higher fiber content in lowerTiO₂-containing papers (i.e. equivalent basis weight). In this mannerthe total amount of WSR was held constant at 0.75% dry polymer solidsweight relative to dry fiber weight. Hand sheets were formed from acommercial lab scale unit.

Hand Sheet Properties:

Wet Tensile Strength Measurements.

Strips cut from hand sheets (40% TiO₂ content) were mounted andmoistened on a TT-2703 horizontal tensile tester and the force appliedto breakage was measured for each strip according to ISO 1924-2. Table 1reports the average tensile strength from 5 strips. At equal pigmentloading, décor papers made with cationized TiO₂ pigment dispersion hadwet tensile strengths no worse than paper made with comparative pigmentdispersion.

TABLE 1 Dry Ash Wet Tensile Strength basisweight (% Average of 5 stripshandsheet (gsm) TiO2) (Newton) (SD) Control A 102 40.3 2.58 0.54 Example1 A 111.2 40.5 2.92 0.46 B 112.7 41 3.11 0.22Laminate Process & Properties:Creation of a Décor Paper Laminate Panel having Improved Appearance.Step 1: Using a laboratory impregnator, décor paper sheets from abovewere impregnated with a 50% aqueous solution of thermosettingmelamine-formaldehyde resin. The paper sheets were dried andcharacterized by a volatility content of 6.5% by weight. The volatilitycontent was determined by heating the resin-impregnated sheet at 160° C.for five minutes.Step 2: A high pressure laminate sheet plate was made in the laboratoryby stacking five sheets of kraft paper already impregnated with athermosetting phenolic resin, together with the resin saturated sheetfrom Step 1, which is placed on top of the stack. The assembly wasplaced in a heated press and subjected to 150° C. temperature for 40minutes at 10 MPa pressure.Improved Appearance According to the DuPont Appearance Analyzer (DAA).

The appearance of the resulting laminate panels was measured using thecommercially available DAA unit. The unit of measure, the DuPontappearance value (DAV2), quantifies the amplitude of surface peel(roughness) and thus a lower value corresponds to a smoother surface.Results from the table show that at high loading levels (i.e. >36 g/m²TiO₂) there is a trend toward improved appearance in laminate panelsmade from décor paper containing cationized TiO₂ dispersion. However, atlower loading levels, the appearance deteriorated when compared to thelaminated control.

Comparative Example

Process for Titanium Dioxide Slurry Preparation.

A 36.5 wt. % aqueous slurry was made by charging a 500 mL stainlesssteel beaker with 148 g of demineralized water and pH adjusted to9.2-9.4 with the addition of 10% NaOH. 85 g of TiO2 was added by mixingwith a Cowles blade at 1000 rpm. The slurry was then dispersed at 5000rpm for 5 min. using a Dispermat mixer. Stirring was halted while the pHmeasurement was made. Again, pH was adjusted to 9.2-9.4 with theaddition of 10% NaOH with gentle stirring and pH maintained for at least1 minute. Agitation was continued for an additional 10 min. at 5000 rpm.An isoelectric point of 6.5 was measured for the pigment containedwithin.

Hand sheets were prepared by combining pulp-containing thinstock(mixture containing 0.625% pulp solids), 0.75% Kymene 617 (total amountdetermined on a dry solids/dry fiber basis), and adjusting the pH to 6.0with 10% H₂SO₄. To produce a 100 g/m² basis weight sheet containing 40%TiO₂, 312 g of pulp suspension was added to 4.3 g of TiO2 slurry. Anadditional aliquot of Kymene WSR was added at this point to compensatefor the higher fiber content in lower TiO₂-containing papers (i.e.equivalent basis weight). After mixing for 1 min under low shear, handsheets were fabricated using an automatic sheet former.

A laminate panel was produced from the hand sheet according to Step 1and Step 2 above. When the control was compared to the invention,opacity of a laminate panel made with comparative TiO₂ dispersioncontaining 39.7 g/m² TiO₂ by weight demonstrated equal opacity whencompared to a laminate panel made with cationized TiO₂ dispersion. Inthis case 36 g/m² delivered the same opacity (93 by black/white hiding)and contained 10% less pigment by weight (see Table 2).

TABLE 2 Rutile TiO2 with Laminate added basis Opacity Metal weight TiO2Appearance Yblack/ Oxide dry amount DAV2/ Ywhite Content (gsm) (gsm)black (%) Comparative 8% 101.6 39.7 77 92.61 Control 8% 101.6 39.6 8092.18 8% 102.4 36.6 87 92.83 8% 102.7 37.0 79 91.89 8% 102.9 33.3 8890.73 8% 100.5 30.7 100 89.57 8% 103.2 29.3 88 89.05 8% 102.7 28.3 9088.89 8% 103.2 25.0 108 87.46 8% 100.9 22.6 108 85.53 Example 1 16%109.8 40.4 73 95.23 16% 110.3 36.7 81 93.19 16% 110.8 37.7 82 93.72 16%110.6 32.8 104 92.47 16% 112.4 34.1 101 92.24 16% 104.6 23.5 164 85.6816% 105.5 23.4 139 86.98

What is claimed is:
 1. A process for making a décor paper from adispersion with improved optical performance, comprising the steps: (a)combining a treated TiO₂ particle having a surface area of at leastabout 30 m²/g with water and a first cationic polymer to form a TiO₂particle slurry; wherein the treated TiO₂ particle comprises an oxideselected from the group consisting of silicon, aluminum, phosphorus andmixtures thereof; and the oxide is present in the amount of at least 15%based on the total weight of the treated titanium dioxide particle; (b)combining the TiO₂ particle slurry of step (a) with paper pulp and asecond cationic polymer; wherein for equal optical performance, theamount of treated TiO₂ particle in the dispersion is reduced by about10% when compared to the same dispersion not comprising the TiO₂particle slurry of (a).
 2. The process of claim 1 wherein the treatedTiO₂ particle is a pigment.
 3. The process of claim 1 wherein the firstcationic polymer is a urea-formaldehyde resin, a melamine-formaldehyderesin, a cationic polyacrylamide polymer, a polydialkyllammoniumpolymer, a polyacrylamide-polydialkylammonium copolymer, or apolyamide-polyamine-epichlorhydrin resin.
 4. The process of claim 1wherein the second cationic polymer is a urea-formaldehyde resin, amelamine-formaldehyde resin or a polyimide-polyamine-epichlorhydrinresin.
 5. The process of claim 1 wherein the oxide is silicon oxide thatis present in an amount of at least about 6% by weight, based on thetotal weight of the treated TiO₂ pigment.
 6. The process of claim 5wherein the silicon oxide is applied by deposition of pyrogenic silicaonto a pyrogenic TiO₂ particle, co-oxygenation of silicon tetrachloridewith titanium tetrachloride or by deposition via condensed phase aqueousoxide.
 7. The process of claim 6 wherein the silicon oxide is applied bydeposition via condensed phase aqueous oxide.
 8. The process of claim 6wherein the silicon oxide is substantially homogenous on the surface ofthe TiO₂ particle.
 9. The process of claim 5 wherein the silicon oxideis applied by deposition via condensed phase aqueous oxide.
 10. Theprocess of claim 1 wherein the oxide is aluminum oxide that is presentin an amount of about 4 to about 8%, based on the total weight of thetreated TiO₂ pigment.
 11. The process of claim 1 wherein the TiO₂particle has a particle size of about 0.02 to about 0.95 microns. 12.The process of claim 1 wherein the TiO₂ particle has a particle size ofabout 0.5 to about 0.75 microns.
 13. The process of claim 1 wherein theTiO₂ particle is a pyrogenic TiO₂ particle.
 14. The process of claim 1wherein the second cationic polymer is present in the amount of about0.5 to about 1.5% by weight, based on the total dry weight of the pulpused in the paper.